Multilayer polymeric product based on polyethylene terephthalate and polycarbonate and its use as a building material

ABSTRACT

A multilayer polymeric product is described, which consists of a co-extruded internal central layer of polyethylene terephthalate (PET) copolymer, in a quantity ranging from 80 to 90% by weight with respect to the total weight of the internal layer, mixed with polycarbonate (PC), in a quantity ranging from 10 to 20% by weight with respect to the total weight of the layer, and outer, side layers, of a blend of PET, in a quantity ranging from 15 to 25% by weight with respect to the total weight of the outer layers, and PC, in a quantity ranging from 75 to 85% by weight with respect to the total weight of said outer layers, in particular for use as a building material.

The present invention relates to a multilayer polymeric product based onpolyethylene terephthalate and polycarbonate, its relative use as abuilding material and the process for the production of the productitself.

As far as the product is concerned, the objective of the presentinvention is to find an alternative material to polyvinylchloride (PVC)or PMMA in the building industry and glass resin.

Polyethylene terephthalate (PET) is widely used in the production of allkinds of containers, in particular, bottles, extruded film products andsheets for applications in packaging and thermoforming. In its use as abuilding material, however, PET has various significant disadvantagessubstantially due to its poor thermal stability and low resistance tohydrolysis.

It has a low softening point and temperatures around 55° C. are in factsufficient for softening PET (Vicat softening temperature: Method B50:75° C. according to the regulation ISO 306). This limit obviouslygreatly interferes with the use of PET-based structures in the buildingindustry as the high outside temperatures in the summer can reachvalues, such as those indicated above, in correspondence, for example,with connections with metallic profiles, such as aluminum.

The state of the art has therefore attempted to solve this problem bymodifying the properties of PET (see patents such as EP152825,DE2917395, U.S. Pat. No. 4,226,961, EP270374, DE2647565, NL7903118), bythe addition to PET, for example, of polyethylene naphthalate (PEN) orpolycarbonates (PC), in the presence of special additives.

Polycarbonate is in fact characterized by a vicat softening temperatureequal to 156° C. It is a material widely used in the building industry,is versatile, with an excellent dimensional stability, extremelyresistant, with a good processability, relatively resistant toscratches, with excellent optical properties and UV stability.

Unfortunately, however, PC is an extremely expensive material and thisprevents it from being more widely used in the building industry.Furthermore, it has a low resistance to solvents and to some chemicaladditives.

The multilayer polymeric product according to the present inventionallows the drawbacks which characterized the known art to be overcome.

In particular, the objective of the present invention is consequently toprovide a multilayer polymeric product which has a thermal resistance asclose as possible to that of PC, which guarantees a greater resistanceto chemical agents and which, at the same time, has a much lower costthan that of PC, and therefore compatible with use in the buildingindustry, thus overcoming the limits which characterize the known art,obtaining, in our case, an increase in resistance to chemical agentswith respect to PC.

An object of the present invention relates to a multilayer polymericproduct which consists of a coextruded internal central layer, ofpolyethylene terephthalate (PET), in a quantity ranging from 80 to 90%by weight with respect to the total weight of the internal layer, mixedwith polycarbonate (PC), in a quantity ranging from 10 to 20% by weightwith respect to the total weight of the layer, and outer, side layers,of a blend of PET, in a quantity ranging from 15 to 25% by weight withrespect to the total weight of the outer layers, and PC, in a quantityranging from 75 to 85% by weight with respect to the total weight ofsaid outer layers.

The outer layers are an upper layer and a lower layer with respect tothe central layer.

The multilayer polymeric product, object of the present patent can havea honeycomb structure or a solid or corrugated structure, as indicatedbelow.

In a particular embodiment, the multilayer polymeric product accordingto the present invention can be made up of 4 (four) layers, an internalcentral layer, two outer side layers and an overall outer layer for thewhole system containing a specific UV protection.

The internal central layer is preferably a blend of PET, in a quantityequal to 90% by weight with respect to the total weight of said layer,and PC, in a quantity equal to 10% by weight with respect to the totalweight of said layer, and the two outer side layers are a blend of PET,in a quantity equal to 20% by weight with respect to the total weight ofthe two outer layers, and PC, in a quantity equal to 80% by weight withrespect to the total weight of said layers.

In particular, the central layer has a thickness from five to seventimes the thickness of the outer layer, preferably a thickness equal tosix times the thickness of the outer layer.

A further object of the present invention relates to a process for theproduction of a multilayer polymeric product which consists in acoextruded internal central layer of polyethylene terephthalate (PET),in a quantity ranging from 80 to 90% by weight with respect to the totalweight of the internal layer, mixed with polycarbonate (PC), in aquantity ranging from 10 to 20% by weight with respect to the totalweight of the layer, and outer, side layers, of a blend of PET, in aquantity ranging from 15 to 25% by weight with respect to the totalweight of the outer layers, and PC, in a quantity ranging from 75 to 85%by weight with respect to the total weight of said outer layers, saidprocess comprising the following phases:

-   -   i) the PET, possibly containing additives, is subjected to        drying and regradation;    -   ii) the PC, possibly containing additives, is subjected to        drying;    -   iii) the PC/PET blend, possibly containing additives, is        subjected to drying;    -   iv) PET and PC are subjected to blending at a temperature        ranging from 80 to 140° C.;    -   v) the blended product is charged into the main extruder and        extrusion is effected of the internal layer at a pressure        ranging from 70 to 450 atm and a temperature ranging from 250 to        350° C.;    -   vi) the blend coming from phase iii) is extruded to give the two        outer layers;    -   vii) the three layers coming from phases v) and vi) converge in        a coextruder where they are coextruded at an increasing pressure        from 70 to 450 atm and a temperature varying from 230 to 270° C.        and then stabilized;    -   viii) the multilayer product coming from phase vii) is subjected        to calendering and thermoforming with by-step thermal cycles        within a range of 10 to 140° C.

A further object of the present invention also relates to the use as abuilding material of a multilayer polymeric product which consists in acoextruded internal central layer of polyethylene terephthalate (PET),in a quantity ranging from 80 to 90% by weight with respect to the totalweight of the internal layer, mixed with polycarbonate (PC), in aquantity ranging from 10 to 20% by weight with respect to the totalweight of the layer, and outer, side layers, of a blend of PET, in aquantity ranging from 15 to 25% by weight with respect to the totalweight of the outer layers, and PC, in a quantity ranging from 75 to 85%by weight with respect to the total weight of said outer layers.

The product has an overall quantity of PC equal to 10-20% of the totalweight of the product.

A first important advantage of the product and process according to thepresent invention consists in the production of said product by means ofan integrated production process, wherein all the production phases arecarried out on line and in continuous. This process guarantees areduction in the production costs and, contemporaneously, an increase inthe intrinsic quality of the product.

Thanks to the production process according to the present invention, anincrease in the technical characteristics and mechanical resistance ofthe product are obtained, even in the presence of a reduced percentageof PC (within 10-20% of the total weight of the product) with respect tothe quantity of PC necessary for obtaining the same performances,adopting traditional production systems.

Furthermore, the production process according to the present inventionallows PC and PET to be combined without the use of additives orcompacting agents, but adopting a process in continuous, the applicationof different temperature sequences in the various production cycles(from 80 to 350° C.) and different section pressures ranging from 250 to450 atm. The above process in particular envisages the application ofthe above “By-step” temperatures and pressures, i.e. not in continuous.

A fundamental advantage of the multilayer polymeric product according tothe present invention is that it has a thermal stability comparable tothat of PVC, PMMA, having the advantage however of guaranteeing agreater flame resistance; in the case of combustion, an inflow ofnon-harmful fumes and a greater mechanical resistance to high and lowtemperatures. The internal layer is in fact already stable totemperatures in the order of 70° C. and is further protected by theouter layers, richer in PC, which are stable up to temperatures in theorder of 110-120° C.

A further advantage of the multilayer polymeric product according to thepresent invention consists in the high compatibility between the outerlayers and the internal layer: this compatibility makes the structureextremely solid, making detachment between the central internal layerand outer side layers, practically impossible.

Another important advantage of the multilayer polymeric productaccording to the present invention is the following. Due to theparticular process used in the production of the multilayer polymericproduct, there is a bleeding effect of the PC: i.e. a gradual variationtakes place in the concentration of the PC in the transition areasbetween the internal layer, which is less rich in PC, and the outerlayers, richer in PC.

This gradual variation in the concentration of the PC also causes agradual variation in the temperature resistance in the transition areasbetween the internal layer, which is less rich in PC, and the outerlayers, richer in PC. This therefore creates a high elasticity of themultilayer polymeric product according to the present invention.

This effect is clearly visible in FIGS. 1 and 2 which are a photographof the multilayer polymeric product according to the present invention.FIG. 1 shows the central internal layer and the upper outer layer(darker), FIG. 2, shows the central internal layer and the lower outerlayer (darker).

In both figures, in fact, the darker area is the outer layer richer inPC, whereas the lighter area corresponds to the central internal layer,less rich in PC. An intermediate-coloured transition area can be clearlyseen, where there is the bleeding effect of the PC between the lightarea and the dark area.

Furthermore, the multilayer polymeric product according to the presentinvention does not require preparation of the blends in mass, asdescribed in all the documents of the known art (for example in patentsEP152825, DE2917395, U.S. Pat. No. 4,226,961, EP270374, DE2647565,NL7903118), which would require the use of extremely complex equipment.In the process according to the present invention, in fact, it is notnecessary to effect a pre-blending of the components as there is acontinuous cascade processing flow.

The main advantage of the multilayer polymeric product according to thepresent invention consists in the fact that, with a total quantity of PCranging from 10 to 20% by weight with respect to the total, it has atemperature stability equal to that of a blend containing 50-60% byweight of PC with respect to the total.

The multilayer polymeric product according to the present inventionallows both honeycomb and solid corrugated structures to be produced.

Furthermore the multilayer polymeric product has the followingadditional advantages.

The different softening temperature creates an induced self-tensionsystem which compensates the tensions created by the external pressureloads. As the two tension systems annul each other, they allow the sheetto resist higher loads with respect to a sheet of an equal thicknessproduced with single-layered extrusion. This gives a higher resistanceto external loads.

As the outer layers have better temperature resistance characteristics,they preserve the material they enclose, increasing its temperatureresistance due to the shield effect. The outer material, in fact, has alow thermal conductivity coefficient, i.e. it limits the passage of heatby contact (induction) and, thanks to the presence of an additive whichreflects infrared rays, a lesser heating of the surface of the sheet isobtained. This produces a higher operating temperature.

As the outer layers have better temperature resistance characteristics,they preserve the material they enclose, increasing its temperatureresistance due to the containment effect. The softening of the weakercentral material would normally cause the viscous deformation of thesheet but this is prevented by the outer presence of a material whichpreserves its mechanical characteristics. This produces a higheroperating material.

The surface temperature is kept lower thanks to the presence inextrusion of a layer of material with a high reflecting power which, byreflecting the solar radiation infrared component, allows two advantagesto be obtained: 1) an increase in the operating temperature of the sheetas the performance increases with respect to direct exposure, 2) adecrease in the greenhouse effect inside the construction. This producesa higher operating temperature.

The protection offered by the outer material, having a greaterresistance to hydrolysis, preserves the PET-based internal material fromhydrolysis. This characteristic makes the product more long-lasting withrespect to a single-layered product. This produces a longer duration.

The various refraction indexes of the different layers produce, as aresult of the reflection of light rays, a better and greater lightpassage: better as there is the characteristic of uniformity and highdiffusion, greater as the value is higher with respect to the lightpassage of the single-layered sheet. This produces a greater lightpassage.

In particular, the multilayer polymeric product according to the presentinvention, either with a honeycomb structure or with a solid and/orcorrugated structure, can be used as a building material forgreenhouses, extended building, skylights, canopies, horizontalsheathing, protection systems.

The honeycomb structure has a greater resistance and greater insulatingproperties.

In particular, the multilayer polymeric product according to the presentinvention preferably has a thickness varying from 4 to 16 mm in the caseof honeycomb structures, a thickness varying from 0.5 to 5 mm in thecase of solid structures and a thickness varying from 0.5 to 3 mm in thecase of corrugated structures.

The internal layer of the multilayer polymeric product according to thepresent invention preferably has a thickness varying from 500 to 700microns, the outer layer preferably has a thickness varying from 50 to150 microns and the outer UV protection layer, when envisaged,preferably has a thickness varying from 20 to 60 microns.

The polyethylene terephthalate preferably has an intrinsic viscosityranging from 0.83 to 1.20 dl/g, preferably close to 1 dl/g.

The polycarbonate (PC) can be any PC, i.e. linear or branched PC with anMFI value (melt flow index)-according to the regulation ASTM D1238—which varies from 4 to 12 g/10 min., preferably equal to 7 g/10min; and an intrinsic viscosity varying from 1.2 to 1.4 dl/g, preferably1.3 dl/g—according to the regulation ISO 1628-4.

Furthermore, the multilayer polymeric product according to the presentinvention can be coloured and can contain various additives such asprotection additives against UV aging, infrared ray reflecting layers,various gradations of master-batches, depending on the particularcharacteristics of use of the end-product.

In particular, the multilayer polymeric product according to the presentinvention can variously contain mica powder and compatibilizingadditives to obtain a heat reflecting effect and consequently lower thecontinuous operating temperature of the sheet.

The process for the production of the multilayer polymeric productaccording to the present invention allows the bleeding effect of the PCdescribed above to be obtained specifically as a result of theparticular thermal cycles envisaged in the four-layered co-extrusion.

In the coextrusion, the “by-step” pressures within a range of 70 to 450atm, cause a bleeding phenomenon between one layer and another,eliminating problems of delamination and improving the mechanicalcharacteristics of the product.

Furthermore, the “by-step” thermal processes carried out within a rangeof 10 to 140° C., to which the product is subjected (the two outerlayers are shaped below the softening temperature, whereas the internallayer is folded at a temperature higher than the softening point) causetensioning in the two outer layers with a consequent increase in themechanical resistance of the sheet.

In particular, the process according to the present invention envisagesthat all passages be carried out on line and in continuous.

Furthermore, the process according to the present invention envisages,in the coextrusion, that the pressures vary “by-step” within a range of70 to 450 atm, generating bleeding and that the thermal processes becarried out “by-step” within a range of 10 to 140° C., causingtensioning between the layers.

In particular, the process according to the present invention can alsoenvisage the coextrusion of a fourth outer layer consisting of a PC/PETblend with a UV-ray protection additive.

The characteristics and advantages of the multilayer polymeric productand process according to the present invention can be better understoodfrom the following detailed and illustrative description referring tothe following figures and examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 shows the central internal layer and the upper outer layer(darker);

FIG. 2 shows the central internal layer and the lower outer layer(darker);

FIG. 3 shows a plan view of a line for effecting the process accordingto the present invention in one of its embodiments;

FIG. 4 shows a raised partially sectional side view of a line foreffecting the process according to the present invention in one of itsembodiments.

FIG. 5 is a legend of the contents of FIG. 4.

FIG. 6 is a graph concerning the elastic modulus of the multilayerpolymeric product (MPP) that graphically represents the resistance ofMPP at increasing temperature in comparison with a sheet of PET.

FIG. 7 is a graph showing the behavior to hailstone at room temperature.MPP behavior is compared with the behavior of a PET sheet.

FIG. 8 is a graph which compares the behavior of MPP to PET whencontacted with sphere of 40 mm.

FIG. 9 shows the correlation between the value of Light Transmission in% and exposure to sun in hours where the performance of MPP and a PETsheet are compared.

With reference to FIGS. 3 and 4, these indicate with a high-speedextruder coupled with screws with particular profiles, with a highmixing power at high pressure, with B a mixer with an extruder feeder;with C and D coextrusion extruders, with E a UV protection extruder,with F equipment for the homogenization of the various layers andrelative compacting with a bleeding effect of the various polymers; withG a multilayer extrusion head, with H a calender with the possibility ofregulating the operating temperature from 10 to 140° C.; with I and Lthermoforming systems in continuous with temperatures ranging from 10 to140° C., with M, N, O and P standard accessories of the extrusion linessuch as multiple pull systems, polythening sheet application, sheetcutting and stacking.

1, 2 and 3 indicate blending stations of the raw materials, 4, 5, 6, 7,8 and 9 systems for the drying, dehumidification and regradation of theraw material or product.

For greater clarity see the enclosed legend as FIG. 5.

In a particular embodiment, the process according to the presentinvention effected on line described above comprises the followingphases. The polyethylene terephthalate (PET) (intrinsic viscosity indexfrom 0.80 to 1.20 dl/g) with the presence of stabilizers and slip agents(such as phosphite/phenol and waxes), is subjected in the station 7 ofFIG. 3 to a drying process until it reaches a residual humidity lowerthan 50 ppm. A regradation process is then initiated, which improves itsintrinsic viscosity, ideally stabilized at 1.0 dl/g. The linear orbranched polycarbonate (PC) (intrinsic viscosity index from 1.2 to 1.4dl/g) with the presence of process additives (such as phosphite/phenol),is subjected in station 8 of FIG. 3 to a drying process. Drying of thePC/PET blend is then effected in station 9 of FIG. 3 at 180° with aUV-ray protection additive (benzotriazole).

In sections 1-2-3 of FIG. 3, the temperature passes from 80 to 140° C.:at this point the mixing between PET and PC is effected.

The product is charged into the extruder starting from section “B”. Inthe first section of the high mixing screw (“B1”) the maximum pressureof 450 atm and the maximum temperature of 350° C. are reached. In theremaining sections of the screw, before the station “F”, the temperatureis reduced to the normal operating temperature (250-300° C.) and thepressure drops to 70-150 atm.

The coextrusion of the product coming from the main extruder takes placein the station “F”: the stations 4 and 5, relating to the outer layers,are fed by the apparatuses 7-8-9. The three flows converge in the centreof the coextruder “F” where they are coextruded and stabilized in thestructure. The bleeding of the three layers is obtained thanks to theincreasing pressures up to the maximum value.

In the extrusion head “G”, the temperature falls to 230-270° C. and theproduct is extruded. Finally in the calender “H” and in thethermoforming stations “I” and “L”, the product is subjected to“by-step” thermal cycles within a range of 10 to 140° C. through whichthe sheet is thermoformed and stabilized in its definite shape andcharacteristics. The stations M-N-O-P represent standard parts of theextrusion lines with pulling systems, polythening, cutting and stacking.

An applicative and non-limiting example of a product according to thepresent invention is provided hereunder, in particular an example of theproduction of a compact corrugated sheet.

EXAMPLE

A solid corrugated sheet was produced with the method described above:

polymeric product according to the present invention are specifiedbelow:

a) Operating Temperature

The following values are obtained with a dynamo-mechanical analysistest, method DMA 7 (free point bending) carried out for a comparisonwith PET and with the multilayer polymeric product according to thepresent invention: for PET, once the intrinsic TG of PET has beenexceeded (78° C.), the modulus falls and the values are no longermeasurable; for the multilayer polymeric product according to thepresent invention, even after exceeding the intrinsic TG of PET (78°C.), the modulus remains at around a value of 600 MPA over 100° C. (seeFIG. 6).

b) Mechanical Resistance:

The following values are obtained with a hailstone resistance test atroom temperature and at 0° C., carried out according to the regulationUNI 10890/2000 on sheets of PET and on the multilayer polymeric productaccording to the present invention:

-   -   i) at room temperature (see FIG. 7)    -   for PET, breakage at about 27 m/s=Group V10A;    -   for the multilayer polymeric product according to the present        invention: breakage over 36 m/second=Group V14A.    -   ii) at 0° C. (see FIG. 8)    -   for PET, breakage at about 20 m/s=Group V8A;    -   for the multilayer polymeric product according to the present        invention: breakage over 65 m/second=Group V10A.

c) Resistance to Hydrolysis:

The following values (see FIG. 9) are obtained with the QUV test 340 nm(cycle of 20 hours at 60° C.+4 hours condensation at 50° C.) to detectthe light transmission after 1000 hours of aging, carried out forcomparison, on sheets of PET and on the multilayer polymeric productaccording to the present invention:

-   -   for PET: light transmission before aging: 88.89; to be compared        with the value of 67.91 after exposure of 1000 hours, following        hydrolysis.    -   for the multilayer polymeric product: light transmission before        aging: 88.9; to be compared with the value of 87.5 after        exposure of 3000 hours.

1. A multilayer polymeric product which consists of a co-extrudedinternal central layer of polyethylene terephthalate, in a quantityranging from 80 to 90% by weight with respect to the total weight of theinternal layer, mixed with polycarbonate, in a quantity ranging from 10to 20% by weight with respect to the total weight of the layer, and twoouter, side layers, of a blend of polyethylene terephthalate, in aquantity ranging from 15 to 25% by weight with respect to the totalweight of the outer layers, and polycarbonate, in a quantity rangingfrom 75 to 85% by weight with respect to the total weight of said twoouter layers.
 2. The multilayer polymeric product according to claim 1,characterized in that the overall quantity of polycarbonate is equal to10-20% of the total weight of the product.
 3. The multilayer polymericproduct according to claim 1, characterized in that the central internallayer is made of polyethylene terephthalate, in a quantity equal to 90%by weight with respect to the total weight of said layer, in a blendwith polycarbonate, in a quantity equal to 10% by weight with respect tothe total weight of said layer, and the two outer side layers, are ablend of polyethylene terephthalate, in a quantity equal to 20% byweight with respect to the total weight of the two outer layers, andpolycarbonate, in a quantity equal to 80% by weight with respect to thetotal weight of said layers.
 4. The multilayer polymeric productaccording to claim 1, characterized in that the internal layer has athickness of five to seven times the thickness of the outer layer. 5.The multilayer polymeric product according to claim 1, characterized inthat it has a thickness ranging from 4 to 16 mm in the case of honeycombstructures, a thickness ranging from 0.5 to 5 mm in the case of solidstructures and a thickness ranging from 0.5 to 3 mm in the case ofcorrugated structures.
 6. The multilayer polymeric product according toclaim 1, characterized in that the internal layer has a thicknessvarying from 500 to 700 microns.
 7. The multilayer polymeric productaccording to claim 1, characterized in that the two outer layers eachhave a thickness varying from 50 to 150 microns.
 8. The multilayerpolymeric product according to claim 1, characterized in that it has 4layers: a central internal layer, two outer side layers, and an outer UVprotection layer.
 9. The multilayer polymeric product according to claim8, characterized in that the outer UV protection layer has a thicknessvarying from 20 to 60 microns.
 10. The multilayer polymeric productaccording to claim 1, characterized in that the polyethyleneterephthalate has an intrinsic viscosity ranging from 0.83 to 1.20 dl/g.11. The multilayer polymeric product according to claim 1, characterizedin that the polycarbonate is a linear or branched polycarbonate.
 12. Themultilayer polymeric product according to claim 1, characterized in thatthe polycarbonate has an intrinsic, viscosity ranging from 1.2 to 1.4dl/g.
 13. The multilayer polymeric product according to claim 1,characterized in that it is coloured and/or contains various additivesselected from protection additives against UV aging, and infrared-rayreflecting layers and master batches.
 14. The multilayer polymericproduct according to claim 1, characterized in that it contains variousadditives, mica powder and compatibilizing additives.
 15. The multilayerpolymeric product according to claim 1, characterized in that it has ahoneycomb structure or a solid structure and a flat or a corrugatedstructure.
 16. The multilayer polymeric product according to claim 1,characterized in that the outer layer has a greater resistance tohydrolysis with respect to the inner layer.
 17. The multilayer polymericproduct according to claim 1, characterized in that the various layershave different refraction indexes.
 18. The multilayer polymeric productaccording to claim 1, characterized in that the internal layer has athickness six times the thickness of the outer layer.
 19. The multilayerpolymeric product according to claim 1, characterized in that thepolyethylene terephthalate has an intrinsic viscosity equal to 1 dl/g.20. The multilayer polymeric product according to claim 1, characterizedin that the polycarbonate has an intrinsic viscosity equal to 1.3 dl/g.21. A method of using as a building material a multilayer polymericproduct which consists of a coextruded internal central layer ofpolyethylene terephthalate, in a quantity ranging from 80 to 90% byweight with respect to the total weight of the internal central layer,mixed with polycarbonate, in a quantity ranging from 10 to 20% by weightwith respect to the total weight of the central layer, and outer, sidelayers, of a blend of polyethylene terephthalate, in a quantity rangingfrom 15 to 25% by weight with respect to the total weight of the outerlayers, and polycarbonate, in a quantity ranging from 75 to 85% byweight with respect to the total weight of said outer layers.
 22. Amethod according to claim 21, wherein the multilayer polymeric producthas a honeycomb structure or a solid structure and a flat or corrugatedstructure and is used for building greenhouses, extended building,skylights, canopies, horizontal sheathing, or protection systems.